1. Field of the Invention
The invention relates to a method and apparatus for cleaning workpieces and, more particularly, to a technique for cleaning workpieces such as automobile engine blocks wherein workpieces are passed through chambers where cleaning media is directed against the workpieces.
2. Description of the Prior Art
Parts such as automobile engine blocks commonly are formed by casting molten metal in a mold comprised of sand and binding agents. After the metal has cooled and the sand mold has been removed from about the parts, a thin layer of sand and other residue remains on the surface of the parts. It is necessary to clean the surface of the parts before the parts can be processed further. An especially effective technique for cleaning the surface of cast parts has been by blast cleaning.
In the blast cleaning process, workpieces are passed through a chamber where cleaning media such as steel shot is thrown against the outer surface of the parts. So-called blast wheels have been used to throw quantities of shot. Typically, blast wheels include a plurality of radially extending paddles. Upon introducing shot particles near the base of the paddles, the shot will be flung outwardly at a high rate of speed by the paddles. By directing the stream of cleaning media in appropriate directions, all surfaces of a workpiece can be blasted free of sand or other surface particles. An especially effective technique for blast cleaning continuously fed parts such as automobile engine blocks and the like is disclosed in U.S. Pat. No. 3,903,652, "Continuous Cleaning Apparatus," issued to Davis L. Baughman and James H. Carpenter, Jr. on Sept. 9, 1975, the disclosure of which is incorporated herein by reference. Other related developments are disclosed in U.S. Pat. No. 3,626,641, "Continuous Cleaning Apparatus," issued to George W. Powell et al on Dec. 14, 1971 and U.S. Pat. No. 3,748,787, "Workpiece Treating Apparatus," issued to James H. Carpenter et al on July 31, 1973, the disclosures of which are incorporated herein by reference.
The referenced patents disclose a technique for cleaning cast parts such as automobile engine blocks by impinging cleaning media upon the parts. The parts are pushed end to end in a line through a rotating barrel open at both ends. The barrel relatively closely conforms to the contour of the parts to be cleaned. Blast wheels located about the circumference of the barrel enable exposed surfaces of the workpieces to be cleaned in relatively short periods of time and with the use of a relatively small number of blast wheels. In effect, a blast stream is impacting the workpieces at all times. Because the barrel is rotated continually, internal passages in the workpieces are drained of cleaning media so that new impacts are not masked by retained media and also so that a new surface is presented to the media at all times. The device referred to is relatively easy to automate and delivers cleaned parts in a position for convenient automatic handling.
One disadvantage of the referenced device is that it is essentially a "one-part" machine, that is, the barrel must be designed to closely fit a particular size of workpiece being moved through the barrel. Also, because the workpieces are pushed against each other, it is difficult or impossible to clean the ends of the workpieces. Although several concepts have been devised to clean the ends of the workpieces (see especially the '641 and '787 patents referred to above), all existing devices are rather complex. In effect, a machine suitable for processing only one size of workpiece is provided.
Although the referenced devices are excellent for cleaning parts of one size at a high rate of speed, there is a need for a machine to clean parts of various sizes and which is easy to automatically load and unload. Desirably, an improved device would be able to utilize existing blast wheels and other equipment as much as possible in order to maximize cleaning efficiency and minimize expense of manufacture. A desirable machine would dispose blast wheels about the periphery of the workpieces in order to eliminate the complexity of rotation of prior devices and to eliminate the need for a close-fitting barrel. Preferably, an improved device would create a gap between parts in order to enable the ends of the parts to be cleaned and would enable cleaning media to be drained from internal passages in the parts.